This invention relates to dilatation catheters and stents for dilating structures or stenoses in the human body. More particularly, the invention relates to balloon catheter and stent delivery systems which have increased flexibility and kink resistance, and which may also have a reduced cross section at the balloon and stent prior to inflation of the balloon.
The use of balloon catheters to treat structures, stenoses, or narrowings in various parts of the human body is well known in the prior art. Examples of such catheters are shown in Bonzel U.S. Pat. No. 4,762,129, Yock U.S. Pat. No. 5,040,548, Kanesaka U.S. Pat. No. 5,330,499, Solar U.S. Pat. No. 5,413,557, and Tsukashima et al. U.S. Pat. No. 5,458,639.
An illustrative procedure involving balloon catheters is known as percutaneous translumenal coronary angioplasty, which may be used to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. This procedure involves passing a balloon catheter over a guide wire to a stenosis. Once positioned appropriately (e.g., under fluoroscopic guidance), the balloon is inflated, which breaks the plaque of the stenosis and causes the arterial cross section to increase. Then the balloon is deflated and withdrawn over the guide wire.
In many cases, a stent must be implanted to provide permanent support for the artery. When a stent is to be implanted, the usual practice is to first dilate the stenosis with a first balloon catheter that does not carry a stent. Then the first catheter is withdrawn over the guide wire and a second catheter which does carry a stent on its balloon is inserted via the guide wire. When the balloon of the second catheter is at the location of the stenosis, that balloon is inflated to circumferentially expand and thereby implant the stent. Thereafter, the balloon of the second catheter is deflated and the second catheter and the guide wire are withdrawn from the patient.
Rapid exchange balloon catheters are those that facilitate rapid removal and replacement of catheters on a guide wire. After a first catheter has been placed in the patient on the guide wire, the physician may wish to remove that catheter and replace it with another catheter having a larger dilatation balloon or an implantable stent as described above. The guide wire is left substantially in place during these catheter removal and replacement steps. To facilitate rapid removal and replacement of catheters, catheters have been designed with relatively short guide wire lumens (e.g., Kanesaka U.S. Pat. No. 5,330,499 and Solar U.S. Pat. No. 5,413,557), which decrease frictional resistance and eliminate the need for extension guide wires that may be necessary when longer guide wire lumens are used. For example, by providing only a relatively short guide wire lumen at or in the vicinity of the balloon, the length of the guide wire outside the patient can be made considerably shorter than if the guide wire lumen extends along the entire length of the catheter. (Some length of guide wire must be outside the patient and outside the catheter guide wire lumen at substantially all times so that a grip can be maintained on the guide wire.) In particular, the length of the guide wire outside the patient can be made only slightly longer than the length of the relatively short guide wire lumen. This makes it possible to shorten the stroke of a catheter being withdrawn (because it is only necessary to withdraw the distal end of the guide wire lumen past the proximal end of the shorter guide wire). Similarly, the stroke of the replacement catheter can be greatly shortened (because it is only necessary to begin feeding the distal end of the replacement catheter's guide wire lumen onto the proximal end of the shorter guide wire). Shortening the two catheter strokes in this way greatly speeds up the catheter removal and replacement operation, leading to the characterization of this type of catheter as a "rapid exchange" catheter.
The rapid exchange balloon catheters in the prior art include multi-lumen (Solar U.S. Pat. No. 5,413,557) or coaxial lumen (Kanesaka U.S. Pat. No. 5,330,499) designs at the balloon site. The result of these designs is a relatively large cross-section balloon region due to the extra lumen through which the guide wire passes. Because of the larger cross section, the balloon catheter may encounter greater resistance while negotiating a tortuous body passageway or vessel. In addition, the balloon may resist entering a stenosis, possibly bunching or folding when attempting to make such entry. If a stent is mounted on the balloon, the stent may cause the cross section to be even larger, thereby exacerbating these problems.
One way to decrease the balloon catheter cross section is to eliminate the extra guide wire lumen at the balloon site. A 1962 article by Nordenstrom may suggest this possibility. Nordenstrom shows a catheter with a guide wire exiting a guide wire lumen distal of the balloon. In Nordenstrom's disclosure, however, the guide wire is not restricted adjacent the balloon. This may be undesirable, and so subsequent catheter designs (e.g., the above-mentioned Solar and Kanesaka designs) contained the movement of the guide wire by extending the guide wire lumen to a point proximal of the balloon.
In view of the foregoing, it is an object of this invention to provide improved catheters and methods for use with guide wires and stents.
It is a more particular object of this invention is to provide balloon catheters having a smaller cross section at the balloon than those in the prior art, and which are more easily and rapidly placed on or removed from guide wires.